General and special purpose host computers often include provisions for various peripheral functionality, such as a communications modem, memory expansion, or an add on hard disk drive. In order to facilitate the addition of various peripherals the Personal Computer Memory Card International Association (PCMCIA) has endeavored to standardize a family of peripheral interfaces. The PCMCIA defined parameters can be found in the PC Card Standard Release 2.0 document, published by the Personal Computer Memory Card International Association, 1030B East Duane Avenue, Sunnyvale Calif. The defined parameters include physical parameters such as dimensions, input/output connections such as control, address, and data buses, signal parameters such as operating levels and impedances, etc.
To facilitate a logical interface between a host computer bus and a PCMCIA interface port various manufacturers such as Intel have developed PCMCIA slot interface integrated circuits (IC). These ICs facilitate a largely transparent parallel interface from the host computer bus to peripheral functions such as the host port of a universal asynchronous receiver transmitter (UART) like National Semiconductor's NS 16550A or NS 16450. Additionally computer operating system software such as various well known Disk Operating Systems like Microsoft disk operating system (MS-DOS) have been developed and proven to provide a reliable and straight forward logical interface between a host computer and a UART. Additionally, a large pool of applications software including proven communications software that expects to see a UART like host port is available.
For many peripheral functions such as a wireline modem or other relatively passive functions the present interfaces are satisfactory. The manufacturer of the peripheral includes a UART device as the initial portion of the interface to the host computer and receives or provides serial data, respectively, from or to the UART to complete the interface between the host computer and a peripheral function. However, the UART device does require physical space that may not be available, represents an economic burden, and may otherwise be a suboptimum interface for some applications that include resident intelligence in the form of a controller. Some manufacturers have developed proprietary interfaces for the host computer to peripheral interface, particularly when a peripheral controller is present. This may be acceptable in the case of a special purpose host when the manufacturer has control of the host computer hardware and operating system software as well as the peripheral function. However this is not typically the case and does requires extra effort to develop the proprietary interface and assure ongoing compatibility with the operating software of the host.
Clearly a need exists for an interface between a host computer and a peripheral controller that takes advantage of existing host operating systems.